Interleukin-12 (IL-12) is a heterodimeric cytokine (p70) which plays key roles in immune responses by bridging innate resistance and antigen-specific adaptive immunity. Trinchieri (1993) Immunol Today 14:335. For example, it promotes type 1 T helper cell (TH1) responses and, hence, cell-mediated immunity. Chan et al. (1991) J Exp Med 173: 869; Seder et al. (1993) Proc Natl Acad Sci USA 90: 10188; Manetti et al. (1993) J Exp Med 177:1199; and Hsieh et al. (1993) Science 260: 547. Interleukin-12 (IL-12) is a disulfide linked heterodimeric cytokine composed of two independently regulated subunits, p35 and p40. IL-12 is produced by phagocytic cells and antigen presenting cells, in particular, macrophages and dendritic cells, upon stimulation with bacteria, bacterial products such as lipopolysaccharide (LPS), and intracellular parasites. The well-documented biological functions of IL-12 are induction of interferon-y expression from T and NK cells and differentiation toward the TH1 T lymphocyte type. IFN-γ, expression of which is induced by IL-12, is a strong and selective enhancer of IL-12 production from monocytes and macrophages. The cytokine IL-23 is a heterodimer composed of a p19 subunit and the same p40 subunit of IL-12. IL-23, similarly to IL-12, is involved in type 1 immune defenses and induces IFN-γ secretion from T cells. IL-27 is formed by the association of EBI3, a polypeptide related to the p40 subunit of IL-12, and p28, a protein related to the p35 subunit of IL-12. IL-27 promotes the growth of T cells and is thought to play a role in the differentiation of TH1 cells. Pflanz et al., Immunity (2002), 16:779-790.
It has been suggested that, particularly in chronic diseases in which there is ongoing production of IFN-γ, IL-12 production is augmented by IFN-γ. It is presumed that after an infective or inflammatory stimulus that provokes IL-12 production, the powerful feedback loop promotes IL-12- and IL-23-induced IFN-γ to further augment IL-12 production, leading to consequent excessive production of pro-inflammatory cytokines. Furthermore, it has been suggested that IL-27 induces the expression of T-bet, a major TH1-specific transcription factor, and it's downstream target IL-12R β2, independently of IFN-γ. In addition, IL-27 suppresses the expression of GATA-3. GATA-3 inhibits TH1 development and causes loss of IL-12 signaling through suppression of IL-12R β2 and Stat4 expression. Lucas et al., PNAS (2003), 100:15047-15052.
IL-12 plays a critical role in multiple-TH1 dominant autoimmune diseases including, but not limited to, multiple sclerosis, sepsis, myasthenia gravis, autoimmune neuropathies, Guillain-Barré syndrome, autoimmune uveitis, autoimmune hemolytic anemia, pernicious anemia, autoimmune thrombocytopenia, temporal arteritis, anti-phospholipid syndrome, vasculitides, Wegener's granulomatosis, Behcet's disease, psoriasis, psoriatic arthritis, dermatitis herpetiformis, pemphigus vulgaris, vitiligo, Crohn's disease, ulcerative colitis, interstitial pulmonary fibrosis, myelofibrosis, hepatic fibrosis, myocarditis, thyroditis, primary biliary cirrhosis, autoimmune hepatitis, Type 1 or immune-mediated diabetes mellitus, Grave's disease, Hashimoto's thyroiditis, autoimmune oophoritis and orchitis, autoimmune disease of the adrenal gland; rheumatoid arthritis, juvenile rheumatoid arthritis, systemic lupus erythematosus, scleroderma, polymyositis, dermatomyositis, spondyloarthropathies, ankylosing spondylitis, Sjogren's syndrome and graft-versus-host disease. See, for example, Gately et al. (1998) Annu Rev Immunol. 16: 495; and Abbas et al. (1996) Nature 383: 787.
Inhibiting IL-12 overproduction, or inhibiting the production of cytokines such as IL-23 and IL-27 which promote IL-12 production and/or TH1 development is an approach to treating the just-mentioned diseases. Trembleau et al. (1995) Immmunol. Today 16:383; and Adorini et al. (1997) Chem. Immunol. 68: 175. For example, overproduction of IL-12 and the resultant excessive TH1 type responses can be suppressed by modulating IL-12, IL-23 and/or IL-27 production. Therefore, compounds that down-regulate IL-12, IL-23 and/or IL-27 production can be used for treating inflammatory diseases. Ma et al. (1998) Eur Cytokine Netw 9: 54.
IL-12 also plays a role in bone loss diseases, particularly those involving osteoclasts. Osteoclasts are unique multinucleated cells within bone that are responsible for bone degradation and resorption. These are the only cells in the body known to be capable of this function. Osteoclasts have a high capacity for the synthesis and storage of enzymes, including acid hydrolases and carbonic anhydrase isoenzyme II. Osteoclasts share phenotypic characteristics with circulating monocytes and tissue macrophages (N. Kurihara et al., Endocrinology 126: 2733-41 (1990); G. Hattersley et al, Endocrinology 128: 259-62 (1991)). These cells are derived from mononuclear precursors that are the progeny of stem-cell populations located in the bone marrow, spleen, and liver. Proliferation of these stem-cell populations produces osteoclastic precursors, which migrate via vascular routes to skeletal sites. These cells then differentiate. and fuse with each other to form osteoclasts, or alternatively, fuse with existing osteoclasts.
The regulation of osteoclastic formation and activity is only partly understood but it is known that excessive bone resorption by osteoclasts contributes to the pathology of many human diseases associated with excessive bone loss, including periodontal disease, non-malignant bone disorders (such as osteoporosis, Paget's disease of bone, osteogenesis imperfecta, fibrous dysplasia, and primary hyperparathyroidism) estrogen deficiency, inflammatory bone loss, bone malignancy, arthritis, osteopetrosis, and certain cancer-related disorders (such as hypercalcemia of malignancy (HCM), osteolytic bone lesions of multiple myeloma and osteolytic bone metastases of breast cancer and other metastatic cancers).